[1] They are found throughout the world with varying species composition and cover depending on topography, soil characteristics, climate, plant community, microhabitats, and disturbance regimes.

They can be damaged by fire, recreational activity, grazing and other disturbances and can require long time periods to recover composition and function.

Biological soil crusts are most often[3] composed of fungi, lichens, cyanobacteria, bryophytes, and algae in varying proportions.

The most common cyanobacteria found in soil crusts belong to large filamentous species such as those in the genus Microcoleus.

Other common cyanobacteria species are as those in the genus Nostoc, which can also form sheaths and sheets of filaments that stabilize the soil.

[5] Microfungi in biological soil crusts can occur as free-living species, or in symbiosis with algae in lichens.

The morphology of biological soil crust surfaces can range from smooth and a few millimeters in thickness to pinnacles up to 15 cm high.

Thicker and rougher crusts occur in areas where higher precipitation results in increased cover of lichen and mosses, and frost heaving of these surfaces cause microtopography such as rolling hills and steep pinnacles.

Cyanobacteria have filamentous growth forms that bind soil particles together, and hyphae of fungi and rhizines/rhizoids of lichens and mosses also have similar effects.

The increased surface roughness of crusted areas compared to bare soil further improves resistance to wind and water erosion.

However, in warm deserts where biological soil crusts are smooth and flat, infiltration rates can be decreased by bioclogging.

These Aeolian deposits of dust are often enriched in plant-essential nutrients, and thus increase both the fertility and the water holding capacity of soils.

[15] Microorganisms like those that make up biological soil crust are good at responding quickly to changes in the environment even after a period of dormancy such as precipitation.

Desiccation can lead to oxidation and the destruction of nutrients, amino acids, and cell membranes in the microorganisms that make up biological soil crust.

[15][16][17] The cyanobacterium Microcoleus vaginatus is one of the most dominant organisms found in biocrust and is fundamental to the crust's ability to reawaken from dormancy when rehydrated due to precipitation or runoff.

[17] Cyanobacteria are primarily responsible for the pigment and rejuvenation of the crust during environmental changes that result in short spurts of rehydration for the biocrust.

A filamentous cyanobacterium called Microcoleus vaginatus was found to exist in a dormant, metabolically inactive state beneath the surface of the crust in periods of drought or water deficiency.

When inevitably there is a period of insufficient water again, the M. vaginatus is able to return to a dormant state, migrating back down into the crust and bringing the pigment with it.

[18] The presence of biological soil crust cover can differentially inhibit or facilitate plant seed catchment and germination.

Differences in water infiltration and soil moisture also contribute to differential germination depending on the plant species.

Therefore, the presence of biological soil crusts may slow the establishment of invasive plant species such as cheatgrass (Bromus tectorum).

[13] The increased nutrient status of plant tissue in areas where biological soil crusts occur can directly benefit herbivore species in the community.

[6] A recent study in China shows that biocrusts have been an import factor in the preservation of sections of the Great Wall built using rammed earth methods.

Compressional and shear forces can disrupt biological soil crusts, especially when they are dry, leaving them to be blown or washed away.

Thus, animal hoof impact, human footsteps, off-road vehicles, and tank treads can remove crusts, and these disturbances have occurred over large areas globally.

Once biological soil crusts are disrupted, wind and water can move sediments onto adjacent intact crusts, burying them and preventing photosynthesis of non-motile organisms such as mosses, lichens, green algae, and cyanobacteria, and of motile cyanobacteria when the soil remains dry.

[13] Climate change affects biological soil crusts by altering the timing and magnitude of precipitation events and temperature.

Removing stressors such as grazing or protecting them from disturbance are the easiest ways to maintain and improve biological soil crusts.

Other methods, such as fertilization and inoculation with material from adjacent sites, may enhance crust recovery, but more research is needed to determine the local costs of disturbance.